<unit, standard> (SI - International System of Units) The
standard set of units of measurement set by the 11th General
Conference on Weights and Measures in 1960. There are seven
base units: the metre (length), the kilogram (mass), the
second (time), the ampere (electrical current), the kelvin
(temperature), the mole (number of atoms) and the candela
(luminous intensity). These are defined either in terms of
physical properties such as the speed of light or, in the case
of mass, by a "prototype" lump of platinum-iridium kept at
BIPM. Derived units like meters per second (speed) are
formed by combining base units. SI also specifies a list of
prefixes (multipliers like "k" for 1000).